Among general satellite antennas, planar waveguide antennas are to receive satellite broadcasting.
A planar waveguide antenna has a horn-like front end and opened sides, so that one side of the waveguide is vibrated and electromagnetic waves move along the waveguide to be irradiated to the air. Here, since impedance is not matched between the waveguide and the air, some of the waves are reflected and thus not all of the energy is irradiated to the air.
Therefore, a waveguide antenna is designed such that the opening of the waveguide is gradually enlarged so as to match impedance between the waveguide and the air, to thereby maximize the amount of energy irradiated from the opening.
FIG. 1 is a cross-sectional view of a horn of a typical waveguide antenna through which a signal passes. As shown, the horn antenna has an outer opening 2 facing the air and an inner opening 3 from which vibration originates.
The waveguide antenna to receive broadcasting as described above only receives signals and thus has a narrow bandwidth of operating frequency, i.e., from 10.7 GHz to 12.7 GHz.
The operating frequency of existing Ku-band planar waveguide antennas are limited to the reception band from 10.7 GHz to 12.7 GHz or to the transmission band from 13.75 GHz to 14.5 GHz, and thus they are receiving-only or transmitting-only.
A satellite antenna has a different elevation angle and a skew angle depending on where it is located, and thus the type and specification of the antenna should be determined taking into account the skew angle and the elevation angle of a location.
A skew angle refers to a difference between the angle at which low-noise block downconverter (LNB) receives signals and the angle at which a satellite transmits signals, and it differs from location to location since Earth is round.
For example, the latitude and longitude of Perth city in Western Australia is 31° S and 115° E, respectively, and those of Canberra city in Eastern Australia, which is the capital city, is 35° S and 149° E, respectively, and the former has a skew angle of −50° and the latter has a skew angle of −15°, which are quite different.
Therefore, in order for a satellite antenna to respond to the difference in skew angles at different locations, skew angles need to be adjustable. However, the planar waveguide antennas need to be mechanically rotated in order to adjust skew angles, which is cumbersome, requires large space, and is less accurate.